Description

d = fdesign.halfband('type',type) initializes
the filter designer 'Type' property with type.
'type' must be either lowpass or highpass and
is not case sensitive.

d = fdesign.halfband(spec) constructs
object d and sets its 'Specification'
to spec. Entries in spec represent
various filter response features, such as the filter order, that govern
the filter design. Valid entries for spec are
shown below. These options are not case sensitive.

tw,ast (default spec)

n,tw

n

n,ast

where,

ast — attenuation in the
stop band in decibels (the default units).

n — filter order.

tw — width of the transition
region between the pass and stop bands. Specified in normalized frequency
units.

By default, all frequency specifications are assumed to be in
normalized frequency units. Moreover, all magnitude specifications
are assumed to be in dB. Different specification types may have different
design methods available.

The filter design methods that apply to a halfband filter specification
object change depending on the Specification choice.
Use designmethods to determine
which design method applies to an object and its specification choice.
Different filter design methods also have options that you can specify.
Use designopts with the design
method to see the available options. For example:

d = fdesign.halfband(specvalue1,specvalue2) constructs
an object d assuming the default Specification property tw,ast,
using the values you provide for the input arguments specvalue1 and specvalue2 for tw and ast.

d = fdesign.halfband(...,fs) adds
the argument fs, specified in Hz to define the
sampling frequency to use. In this case, all frequencies in the specifications
are in Hz as well.

d = fdesign.halfband(...,magunits) specifies
the units for any magnitude specification you provide in the input
arguments. magunits can be one of

linear — specify the magnitude
in linear units

dB — specify the magnitude
in dB (decibels)

squared — specify the magnitude
in power units

When you omit the magunits argument, fdesign assumes
that all magnitudes are in decibels. Note that fdesign stores
all magnitude specifications in decibels (converting to decibels when
necessary) regardless of how you specify the magnitudes.

Examples

Create a default halfband filter specifications object:

d=fdesign.halfband;

Create another halfband filter object, passing the specification
values to the object rather than accepting the default values for n and ast.

d = fdesign.halfband('n,ast', 42, 80);

For another example, pass the filter values that correspond
to the default Specification — n,ast.

d = fdesign.halfband(.01, 80);

This example designs an equiripple FIR filter, starting by passing
a new specification type and specification values to fdesign.halfband.